Cholesterol gallstones are a common costly disease with a complex incompletely understood pathogensesis [sic] involving genetic and environmental contributions. In general, these stones form in the gallbladder when bile is supersaturated with cholesterol. However, supersaturated bile is not sufficient to produce cholesterol gallstones. The environmental factors which contribute to cholesterol gallstone formation are largely unknown and recent studies indicate that, in humans, unique environmental factors demonstrate a greater than 50% contribution to gallstone formation. Recently we demonstrated that the adaptive immune response contributes greatly to cholesterol gallstone formation. We hypothesize that adaptive immune stimulation is one of the environmental factors contributing to cholesterol gallstones in humans. Based upon the data generated to date a likely biological model for this formation is T-cell mediated damage to the gallbladder wall leading to a progressive loss of function of the gallbladder. The goal of this study is to rigorously characterize how the adaptive immune response contributes to the pathogenesis of cholesterol gallstones. Specifically the aims of this study are: 1. To determine which T-cell subsets contribute to cholesterol cholelithogenesis and to determine if cholelithogenesis can be prevented by immunological manipulation. To accomplish this aim T cell subsets (effector T-cells and regulatory T cells) will be transferred to Rag 2-/- mice. Furthermore, because regulatory T-cells are known to ameliorate numerous T-cell mediated diseases, their ability to prevent cholesterol gallstones will be determined utilizing transfer studies. Finally, because T- cells and lithogenic bile promote a Th1 immune response in the gallbladder the ability of mice deficient in Th1 immunity to form cholesterol gallstones will be analyzed. 2. To mechanistically understand how T-cells promote cholesterol gallstone formation. There are several mechanisms whereby T-cells may promote cholesterol gallstone formation. Since inflammation is known to alter hepatic lipid metabolism and transport I will first determine if T-cells alter the concentration of biliary lipids in hepatic or gallbladder bile. Next, because inflammation and gallbladder wall damage occur concurrently with gallstone formation and because gallbladder cytokine expression is markedly altered in mice possessing T-cells I will be determine if T-cells damage the gallbladder or alter gallbladder contractility in the presence of lithogenic bile. Finally, because nucleation is a key factor in cholesterol cholelithogenesis I will determine if T-cells alter the kinetics of gallbladder bile nucleation. The proposed studies will systematically and mechanistically determine the roll of T-cells and adaptive immunity in murine cholesterol gallstone formation. These studies will provide detailed insight into the pathogenesis of cholesterol gallstones. This murine model should provide a framework with which to explore the role of adaptive immunity and human cholesterol gallstone formation and may alter the way the disease is studied, diagnosed, prevented and treated in humans.